For evaluating the performance of an internal combustion engine and the corresponding engine design development, it is desirable to provide dynamic measurements of the fuel and engine oil consumption during operation of the internal combustion engine. Currently, the available methods for determining oil consumption are primarily (1) the use of a dipstick, (2) the drain-weigh technique, (3) radiometric techniques and (4) sulfur methods. However, there are serious shortcomings particular to each of these methods. In addition there are shortcomings common to all of these methods such as their failure to provide real time analysis of oil consumption and their failure to provide information on related fuel consumption during the engine operation.
With regards to the traditional dipstick and drain-weigh techniques, many hours of engine operation are required before enough oil is consumed to obtain repeatable and predictable measurements using these rather imprecise methods. As an example, it is assumed that an engine operating at 50 miles per hour will consume oil at the rate of approximately 5,000 miles per quart, therefore, accordingly it will consume approximately 0.01 quarts of oil per hour. Due to the excessive periods of operation required before measurements may be made using these techniques, information on the time resolution of engine operation is prohibited. In addition, these techniques are susceptible to a high degree of inaccuracy, since any losses due to oil seal leaks or retention of the oil in other engine parts will lead to an over estimate of oil consumption, while an underestimate of oil consumption may occur due to fuel dissolution with the oil.
An alternative method for determining consumption is known in the art and is based on the monitoring of sulfur dioxide (SO.sub.2), either photometrically or coulometrically, generated from the sulfur in the engine oil during engine operation. This method requires sulfur free isooctane fuel, which therefore undesirably limits the adaptability of this method. In addition, extensive equipment and manpower are required to maintain the test system. Lastly, this method is also subject to interferences from other major or minor exhaust gas components.
The radiometric method is also known and employed by the art. The radiometric method provides a very precise method for measuring oil consumption. This method involves adding the radioactive bromine tracer of 1, 2-dibromooctadecane to the oil. The resultant combustion product from the internal combustion engine is trapped within a sodium hydroxide solution and counted by scintillation counting. This method is undesirable, even though extremely accurate, because of the significant radioactive health and safety considerations and regulatory requirements necessary for its use. In addition, another shortcoming of this method is that it is essentially a batch process which does not readily lend itself to individual measurements, and further requires the preparation of a fresh bromine tracer for each batch operation because of the short half life of the radioactive bromine tracer.
Therefore, there is a definite need in the art for an alternative method for measuring oil consumption during operation of an internal combustion engine in automotive applications. Further, it is desirable that the provided method for determining oil consumption be simple and precise, permit real time measurements and additionally provide concurrent dynamic fuel consumption data.